Paul's tone shifts slightly throughout the novel, depending upon where he is on his happiness-o-meter. The majority of his storytelling efforts are spent describing the atrocities of war, and so his tone is appropriately grim, matching the emotional and physical landscape of the war. When Paul is safe, or when he is eating, a poetic lightness creeps into the language and makes the burden of plowing through this story less heavy.
Take for example the following passage:
He plays mostly folk songs and the others hum with him. They are like a country of dark hills that sing far down under the ground. The sound of the violin stands like a slender girl above it and is clear and alone. (8.29)
"They are a country of dark hills that sing far down under the ground." Way to pull our heartstrings, Paul. Seriously, how gorgeous is that language? It is through moments like these that our storyteller flexes his poetic muscle, and at the same time is able to release some emotion – a rare occurrence in such a tough world.
There is also a fatalism to this writing. Consider Paul's description of Kemmerich's death:
Death is working through from within. It already has command in the eyes. Here lies our comrade, Kemmerich, who a little while ago was roasting horse-flesh with us and squatting in the shell-holes. He it is still and yet it is not he any longer. His features have become uncertain and faint, like photographic plate on which two pictures have been taken. (1.72)
There's again a poetic ring to this description, for our narrator personifies death as a being that is taking control of Kemmerich's body. Remarque often relies on personification to emphasize the soldier's powerlessness when faced with death, and, in so doing, we get the sense that our narrator might well believe in a higher power.
Remarque does not spare us the details of war. He exposes in full light the atrocity of war. In this way, we hear and see his disapproval of the war and his celebration of humanity.